Such apparatus may be used, in particular, in postal sorting installations, e.g. for forming a buffer stock of letters between two sorting machines.
The letters leaving a machine of this type are generally stored in trays which are transported to the following machine. A stack of letters is placed by hand on a support in the form of a right angle trough and having an unstacking device at one end thereof for taking the letters one by one from the stack and placing them at the inlet to conveyor means feeding some other machine. While being conveyed, letters are generally pinched between two endless belts or bands which are guided over rolls along the path to be followed, with the letters being placed between the belts either in an overlapping or roofing tile configuration (with the leading edge of each letter overlapping the trailing edge of the preceding letter), or else the letters are separate from one another.
German patent application 3 237 815 describes apparatus for forming a stack of letters on a trough-shaped support, said apparatus comprising conveyor means for conveying letters to the immediate vicinity of the support, stacking means for stacking the letters on the support, and displacement means for obtaining relative displacement of the conveyor means and the stacking means relative to the support or relative to the stack of letters formed on the support. In this prior apparatus, the stacking means for stacking the letters on the support are pivotally mounted on the end of the letter conveyor means, in such a manner as to be capable of moving away from the stack of letters and causing it to advance, e.g. on arrival of a relatively thick letter.
By virtue, of the stacking means being pivotally mounted on the end of the conveyor means, this prior apparatus is poor at accepting letters which are particularly stiff or particularly thick. This operating defect is further accentuated by the fact that the letter stacking means are oriented at a slight angle relative to the stack of letters and cause the top letters of the stack to be folded.
Finally, the pivoting assembly including the letter stacking means has considerable inertia, thereby preventing a high throughput of letters being conveyed to and stacked on the support.
The object of the invention is to provide apparatus of the same type but avoiding the above-mentioned drawbacks and defects.
More generally, the object of the invention is to provide apparatus for forming a stack of flat objects starting from means which convey these objects one after another in an overlapping configuration or separate from one another, and enabling a stack of variable length to be formed with flat objects being added to or taken from the stack independently, either simultaneously or otherwise.
Another object of the invention is to provide apparatus of this type which is capable of operating at very high throughput.